The present invention relates to an orthopedic implant assembly for use in stabilizing bone members in a desired spatial relationship and correcting bone mis-alignment disorders. In particular, the invention concerns a multi-axial spinal fixation system incorporating an elongated member such as a plate.
In the art of orthopedic surgery, and particularly in spinal surgery, it has long been known to affix an elongated member, such as a plate or rod, to bones in order to hold them and support them in a given position. For example, in a procedure to fuse damaged, diseased, malformed or otherwise abnormal vertebrae, the vertebrae are positioned in a corrected position by a surgeon. An elongated plate is placed adjacent to the vertebral bone, and bone anchors, such as specially-configured screws or bolts, are employed to secure the plate to the bones. With such anchors placement is accomplished by drilling one or more holes in the bone(s), and threading the anchors into the holes. As examples, see U.S. Pat. No. 5,676,666 to Oxland et al., U.S. Pat. No. 5,613,967 to Engelhardt et al., and U.S. Pat. No. 5,603,713 to Aust et al. An anchor can be connected to the bone, as by threading into a vertebral hole, through a plate, or alternatively the plate can be placed in position over or around the anchor after the anchor is connected to the bone. The anchor and plate are then secured to each other to minimize or prevent relative movement. In this way, bones may be spinal held and/or supported in proper alignment for healing.
It has been found desirable for implant systems to have the capability for angular orientation of a bolt or other anchor in multiple planes relative to the elongated member or other fixation mechanisms of the implant system. Such features enable bone anchors to be placed at angles which are optimal for anchoring, thus reducing the chance of loosening, pull-out or other movement of the anchors while not compromising the optimal positioning of the fixation plate. Additionally, such systems alleviate awkwardness frequently found in spinal surgery due to uneven bone surfaces and the abnormality to be corrected and generally require less adjustment to the implant, rendering corrective surgery easier for the surgeon and less traumatic for the patient.
Various approaches have been used to achieve such multi-axial capability. For example, U.S. Pat. No. 5,735,853 to Olerud discloses an implant device in which a bone bolt can occupy different angular positions in relation to a plate by providing a compressible spherical collar which snap-fits around the bolt, which collar is rotatable and tiltable in a spherical opening in a plate insert. The compression fit of the bolt and collar within the plate can present difficulty in assembling the apparatus, particularly in a fluid-prevalent environment.
Another approach is shown in U.S. Pat. No. 5,304,179 to Wagner, which shows a bone screw fixed inside a bushing at an angle with respect to the longitudinal axis of the bushing. The bushing is rotatable within a portion of a connector angled with respect to the axis of the adjoining rod-based instrumentation. The connector is rotatable around the instrumentation axis. The Wagner system permits only discrete positions of a bone screw in three-dimensional space to be achieved, and the bushings add extra length and profile to the construct, as well as extra parts for the surgeon to handle and arrange.
A third approach is shown in U.S. Pat. No. 5,984,924 to Asher et. al., which shows a bone alignment system having an elongated bone alignment member sandwiched between two pairs of washers. Each such pair of washers have corresponding surfaces that mate together in a xe2x80x9cball and socketxe2x80x9d configuration to potentially occupy a plurality of positions. When the shaft of a bone anchor extends through each washer pair, and also through an aperture of the elongated member, the washer pairs enable the shaft to be oriented at various angles relative to the elongated member. This approach also requires a plurality of small parts for handling and assembly during surgery. Further, since the washers in that system lie outside of the elongated member, they increase the thickness of the overall construct, with the attendant increase in the difficulty of use in a small surgical space and in the potential for patient discomfort.
There is therefore a need remaining in the art for a multi-axial bone anchor system which minimizes the number of parts used to engage a bone anchor to an elongated member such as a spinal plate in various angular orientations. There is also a need for a lower-profile, smaller-dimensioned multi-axial bone anchor that allows the positioning of the bone anchor to be adjustable through a continuous range of spatial angles and linear positions with respect to the elongated member.
The present invention provides, in one embodiment, an orthopedic implant system including a plate member for placement adjacent and along one or more bones, such as vertebrae, and having a longitudinal axis. The plate member includes at least one slot substantially parallel to the plate axis, which slot includes a channel portion that extends through substantially the entire longitudinal dimension of the plate member. Also provided is a stabilizer including an opening therethrough substantially bounded by a wall, the opening having a longitudinal axis and the stabilizer further including at least one finger portion extending laterally with respect to the opening axis, wherein said finger portion is received within the plate channel so that the stabilizer opening communicates with the plate slot. A bone bolt having a bone engaging portion, an intermediate portion and a threaded post portion extends through the stabilizer opening and the plate slot so that the bolt""s intermediate portion is adjacent the wall of the stabilizer. Additionally, a washer having a rounded top surface, a bottom surface, and an aperture therethrough adapted for fitting around a portion of the bolt, as well as a nut separate from the washer and having a body portion, a skirt portion, a threaded hole extending through the body portion for threaded engagement with the bolt are provided, and the nut and the washer are coupled together prior to engagement with the bolt.
The nut and the washer may be rotatable with respect to each other and translatable with respect to each other. The nut may include a sleeve portion partially within the nut""s skirt portion and substantially concentric with the nut""s hole. Additionally, the washer can include an undercut having a first diameter within the washer""s aperture, and the nut and the washer are coupled together by inserting the sleeve portion into the aperture and expanding a part of the sleeve portion, which may be an end of the sleeve portion, to a second diameter greater than the diameter of the undercut. The expansion can be caused by swaging, flaring, or other processes.
Other features, advantages and objects will be evident from the following specification.